Peyton Manning has always been a split-second ahead – of the pass rush, of the opposing coordinator, even of his own receivers. Perhaps never in the history of the NFL has there been a quarterback as in tune with his surroundings as Manning was with the Indianapolis Colts. There was no static in the channel, no delayed reaction, no pause of uncertainty.

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Peyton Manning joins the Broncos after 14 years with the Colts. (US Presswire)

With the 2012 NFL draft in the rear-view and Manning's official comeback from neck surgery only a few months away, is it reasonable to think he'll be that same quarterback for his new team, the Denver Broncos? Time is catching up with the legend – not only Father Time, but also reaction time, which is crucial for any passer. Several factors are now eating away at that time advantage, and they may add up to more than the split-second that always seemed to keep Manning upright and victorious.

Rich Gannon, a onetime foe of Manning's, sheds some light on what the future Hall of Famer faces.

Gannon will be the first to tell you he was no Peyton, but at one point he was a quarterback in his late 30s … making a comeback from an injury … with several Pro Bowls under his belt … coming off a raft of double-digit-win seasons … working with a new offensive system on an AFC West team … dealing with high expectations for plenty of points and wins. Sound familiar?

The ex-Raider great passed for 4,689 yards in 2002 and led Oakland to the Super Bowl before a shoulder injury and a long layoff in 2003. Then coach Norv Turner came in with a new plan in 2004, and after a long offseason, Gannon was ready to dominate again.

Didn't happen.

"By the time we played Week 1," Gannon says, "I wasn't prepared."

The Raiders went 2-1 under Gannon, but he felt a step slow. Then the quarterback sustained a serious neck injury and was forced to retire. The Raiders went 5-11.

Gannon isn't worried about the same thing happening to Manning, but he is concerned that what was once so automatic for the former Colts icon is not going to be seamless anymore. At least at first.

"He's coming from out of football for an entire year," Gannon says. "He's had to rehab his back, his neck, his arm. Now there's a new environment and a new system. That's a real challenge."

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A similar layoff was a challenge even for Tom Brady, who came back in 2009 after a year rehabbing from a torn ACL sustained in Week 1 of the 2008 season. Brady was still elite, but his touchdowns dropped from (a ridiculous) 50 to 28, and the Patriots won 10 games – second fewest in his career as the full-time starter. (If you set aside Brady's 2009, he and Manning each have only one sub-12-win full season since 2002.)

Brady, of course, was returning to roughly the same system. Not so for Manning. The split-second advantage he had in Indy was because he was in sync with coaches, receivers and lineman. There likely won't instantly be the case in Denver.

"It can be very unsettling," says Gannon, now an analyst with CBS and Sirius NFL Radio. "As quarterbacks, we're creatures of habit. He had [Colts offensive coordinator] Tom Moore for his entire career. You know the offense inside and out. You have a history."

Not anymore. Manning's starting receivers, Demaryius Thomas and Eric Decker, are talented but young. And the offensive line is new to him – especially with trusted center Jeff Saturday going to Green Bay instead of Denver.

And there's pressure. Not just the literal pressure of the pass rush, but the widely accepted idea that the Broncos are now a serious contender for the AFC crown. Manning is used to that pressure because he placed it upon himself and often delivered. But what about his teammates? Here are Denver's 2011 regular-season wins: Cincinnati, Miami, Oakland, Kansas City, the Jets, San Diego, Minnesota, Chicago. How many playoff teams in there? One, and barely. The defense is strong, but it gave up 40 or more points to Detroit, Buffalo and New England last year. You can't blame Tim Tebow for that. But you can blame Tebow (in part) for a brutal 2012 schedule that includes the Steelers, Texans, Saints, Ravens, Patriots, Falcons, and the improving Panthers. How would last year's Broncos have done against that schedule?

"Peyton's gonna have find out what they can handle," Gannon says. "It's like a new marriage: You've been married 14 years to the same person, and now all of a sudden there's change."

Need more split seconds to worry about? Well, we do not know if Manning can dominate in the cold. NFL.com reports his record in games played in sub-40 degree temperatures is 6-5, with 15 touchdowns and 12 interceptions. Not great. Granted, it's not Manning's fault he led the Colts to home-field advantage in the playoffs so regularly. It was his job to earn and win playoff games inside. But he's only won two road playoff games in his career – at Kansas City in 2003 and at Baltimore in 2006. In Peyton's other four road playoff games, the Colts scored 0, 14, 3 and 17 points. Denver often has relatively balmy temperatures during winter. But this is still an unknown.

And there's Manning's age to consider. Only three quarterbacks have won Super Bowls after turning 36 – Johnny Unitas, Jim Plunkett, and John Elway. None of them came off multiple neck surgeries within a two-year span. Robert Bray, a top spine surgeon, believes Manning will be fine. But he acknowledges there hasn't been a study on whether a top athlete can endure all those surgeries and return to the kind of performance Manning has consistently showed. Manning will be the case study. "To whatever extent he can function now, [the nerve] will continue to improve during the next year or two," Bray says. "And that's as good as the nerve gets."

Finally, and needless to say, Unitas, Plunkett and Elway won their titles in eras where running was at least as important as passing. Manning doesn't have Terrell Davis or Marcus Allen. He has Willis McGahee and Knowshon Moreno. Defenses will be more focused on Manning than those two backs, which is something that wasn't the case for Plunkett and Elway.

Manning is an early favorite for 2012 comeback player of the year, and that storyline would be fun to watch. We all want to see the old Peyton Manning. But the old Peyton Manning made a Hall of Fame career on a split-second advantage that may or may not remain after a year off and multiple surgeries. All we really know is that No. 18 has looked like the old Peyton Manning in non-contact drills. That's a lot to bet an entire franchise on, and as T-shirts sold in the Denver area proclaim, in John Elway's words, "There is no Plan B."